In a repeated measures design, what allows subjects to act as their own controls?

In a repeated measures design, the characteristic that allows subjects to serve as their own controls is the implementation of treatments at different times. This design entails measuring the same participants multiple times under different conditions or treatments. By doing so, researchers can directly compare the effects of those treatments on the same individuals, which helps to control for inter-subject variability that might confound the results.

The key advantage of this design is that any differences observed in outcomes can be more confidently attributed to the treatments themselves rather than to differences between the subjects, since each subject experiences all conditions. This enhances the statistical power of the study and minimizes the influence of extraneous variables, which provides more reliable data concerning the effects of the interventions being tested.

In contrast, the other options do not provide the same level of control or enable effective within-subject comparisons:

• Utilizing a random sampling method refers to how participants are selected for a study rather than how they experience treatments.

• Observing different subjects under various conditions does not allow for within-subject comparisons, as different individuals could have inherent differences affecting the results.

• Evaluating the same group under a single condition does not create a basis for understanding how different treatments affect the same participants since no comparison is made between different treatment conditions for